Workers at CERN. Engineers waiting to enter the doors to the ATLAS detector. ATLAS (A Toroidal LHC Apparatus) is one of six detector experiments at the Large Hadron Collider (LHC) particle accelerator at CERN, near Geneva, Switzerland. It is a broad-range detector that measures all particles and physical processes that emerge during proton collisions within the LHC. The LHC is designed to create high energy substances, such as quark-gluon plasma, thought to have existed very early in the history of the universe. The LHC is scheduled to start operating in May 2008.